Lothor, born Kiya Watanabe (portrayed by Grant McFarland), is an exiled evil ninja master. His history is revealed by the middle of the season during the "Samurai's Journey" three-parter. When Cam Watanabe travels back in time to acquire a great power source, he meets younger versions of his parents and learns of an unheard of uncle, Kiya. Kiya is shown to be loose with the rules, in contrast to his twin brother, Kanoi. However, no one expected Kiya to seek to steal the Samurai Amulet (the great power source) from Cam's mother. Attempting to frame Cam, his plan was foiled and exposed by Kanoi. After Cam defeated Kiya in combat, the sensei of the academy banished Kiya from Earth. Cam realizes the truth, as Kiya proclaims before being banished, "I will take the name of the ancient warrior of evil. From this point, I will be known as Lothor! … I will not forget the part you played in this, Brother! I will have my revenge!" As a student at the Wind Ninja Academy, he wore a yellow and black uniform, implying that he studied under the Earth element.
Lothor spent years in space to slowly build an army of evil space ninja (space aliens trained in the dark ninja arts). He intended to conquer Earth and destroy all the protecting ninja academies with their ninja masters, allowing him to become the ultimate dark ninja master. He also first encountered the bounty hunter, Vexacus, and developed an intense rivalry with him. He also apparently married during his exile, as Kapri and Marah were not blood relatives, though no wife was ever seen or otherwise alluded to.
Before his attack on Earth in the first episode, Lothor had returned to Earth previously in secret (a violation of his former sensei's orders). His purpose on this visit is unknown, but while there, he killed the Bradleys, the adoptive parents of Hunter and Blake Bradley. These two were taken in by Sensei Omino and trained at the Thunder Ninja Academy, which, unfortunately, was the first place attacked by Lothor's army. He captured the Thunder Ninja students and Sensei Omino, and even managed to convince Hunter and Blake Bradley that the Wind Ninja's current sensei, Kanoi, was responsible for their adoptive parents' deaths.
The Wind Ninja Academy, now under the leadership of Sensei Kanoi Watanabe, Lothor's brother, was the next target. Once again, Lothor kidnapped the students of the academy. When they were fighting, Sensei Watanabe turned himself into a guinea pig.
Lothor's victory was short-lived, and he soon realized that three students had escaped the purge of the Wind Ninja Academy (Shane, Dustin, and Tori). Being the only three remaining, they were presented with morphers, allowing them to become Wind Power Rangers. These new Power Rangers foiled Lothor's plans on numerous occasions, and he has sent monstrous warriors after them, but they all fail. Nevertheless, he has always stuck by the evil code for destroying a Power Ranger, that "they must be in their true Ranger form." Lothor has a campy sense of humor, which is often reflected from his frustrations with his monsters/nieces when they fail to best the Power Rangers, or in some predictable occasions (e.g. after making a monster grow, he stares at the camera and asks the audience if they really expected him to make it smaller.) Such fourth wall breaking manifested itself in several other of Lothor's asides (in the season finale, piloting the final giant robot the Rangers would fight, he comments on the battle was the most fun he'd had all season) as well.
In the final episodes of the series, treason and betrayal among Lothor's generals saw them all dying off - at each other's hands or at the hands of the Power Rangers. It was soon revealed that these deaths had all been a part of Lothor's great plan, and that when each had died, their spirits had gone to the "Abyss of Evil". With the help of Cam's stolen Samurai Amulet, Lothor was able to make the Abyss overflow and the dead generals and armies were all released once again, free to destroy the world. Shane was quickly able to destroy the resurrected generals with his Battlizer while the other Rangers tossed the other monsters back into the Abyss. Lothor then managed to use Cam's Samurai Amulet to drain the Rangers of their Ranger powers. Fortunately, Shane, Dustin and Tori were able to use their inner ninja powers to seal him and his deceased army in the Abyss of Evil, saving the planet.
Almost a year later in Power Rangers Dino Thunder episode "Thunder Storm," Lothor escapes from the Abyss of Evil and once again captures the ninja students. He lures the Wind Ninja rangers to a beach where he tricks them into accepting new morphers which make them evil. They are eventually freed by the Thunder Rangers and Cam, who have managed to retrieve their old powers. Lothor then teams up with Mesogog, Dino Thunder's big enemy. After a battle with both Ninja Storm and Dino Thunder, in which both their warriors are defeated, Mesogog ends up fighting Lothor and ends up trapping him in a glass jar. Mesogog's Island Base was destroyed a few months later, and presumably Lothor along with it presumably sending Lothor back to the Abyss of Evil.
Read more about this topic: Villains In Power Rangers Ninja Storm